Floods Buried Keezhadi Settlement Around a Millennium Ago

Archaeological excavations at Keezhadi along the Vaigai river in southern Tamil Nadu have yielded brick structures, canals, floors and pottery that echo descriptions of urban life found in Sangam literature. A new scientific study has now added a crucial environmental timeline, suggesting that large floods buried parts of this settlement a little over a thousand years ago.

Why Dating the Sediments Matters

Keezhadi, located in Sivaganga district, lies on a mound within the Vaigai floodplain. The ancient structures are not visible on the surface but are buried under layers of sand, silt and clay. While artefacts indicate organised habitation, determining when the site was damaged or abandoned requires dating the sediments that covered it. Establishing this timeline helps separate the period of human occupation from later natural events.

Using Light to Measure Time

Researchers from the Physical Research Laboratory and the Department of Archaeology, Tamil Nadu used optically stimulated luminescence (OSL) dating to analyse burial sediments. This technique estimates when mineral grains were last exposed to sunlight. Four sediment samples from two excavation pits were carefully collected and analysed, allowing scientists to calculate when flood deposits sealed the archaeological layers.

Evidence of High-Energy Flooding

The OSL dates span roughly the last 1,200 years and vary with depth, consistent with layered flood deposits. Deeper layers were older, while shallower layers were younger, indicating repeated sedimentation. Fine silty clay was found above brick structures, with coarser sand below, suggesting a high-energy flood event followed by calmer deposition. Based on these results, researchers concluded that the “urban-like” structures at Keezhadi were buried around 1,155 years ago due to major flooding of the Vaigai river.

Imporatnt Facts for Exams

• Keezhadi is an archaeological site on the Vaigai floodplain in Tamil Nadu.
• Optically stimulated luminescence (OSL) dating measures the last exposure of sediments to sunlight.
• The study dates burial sediments, not the construction of structures.
• River floods can bury settlements and alter human habitation patterns.

Climate Context and Archaeological Implications

The findings fit into a broader picture of late Holocene climate variability, during which South Indian rivers alternated between wetter and drier phases and frequently shifted course. The Vaigai now flows several kilometres away from Keezhadi, supporting long-term landscape change. By identifying when flooding buried the site, the study helps archaeologists better interpret Keezhadi’s history and plan future excavations, highlighting how environmental forces have long shaped where people live and how their settlements are preserved.